Zinc-iodine battery-capacitor hybrid device with excellent electrochemical performance enabled by a robust iodine host

From both the cost and safety point of view, aqueous rechargeable zinc-ion based electrochemical energy storage devices are highly attractive as a substitute for lithium-ion batteries. The development of zinc‑iodine battery-capacitor hybrid devices (ZIBCHDs) properly integrated with zinc‑iodine batteries (ZIBs) and zinc-ion hybrid capacitors (ZICs) are desired to endure both the large energy density of ZIBs and the high-power density of ZICs. We demonstrated herein an N-doped porous carbon framework (3D) decorated with nanosheets (2D) hybrids can serve as a robust iodine host. Benefitting from its unique 3D2D microstructure, large BET surface area, and abundant surface functional groups, the resulting porous carbon/iodine cathodes can display battery level specific capacity and energy density as well as a supercapacitor level rate capability and cycle stability. The optimized cathode delivers a large reversible specific capacity of 291.5 mAh g−1 at 0.5 A g−1, which is much larger than the corresponding ZIBs (163.8 mAh g−1) and ZICs (148.9 mAh g−1) revealing the broadening potential window can effectively utilize carbon scaffold to further boost the specific capacity. Additionally, the energy storage mechanism was fully explored through a series of ex-situ testing techniques, and a combination of physical/chemical adsorption-desorption and redox reactions mechanism has been proposed.